Project Summary Human norovirus is the leading cause of acute gastroenteritis globally causing up to 200,000 deaths per year. However, there are no antiviral drugs or vaccines. We use the closely related mouse or murine norovirus (MNV) as a model system to understand how human norovirus causes infection and disease. More broadly, we also use MNV as a tool to uncover novel and fundamental aspects of how viruses interact with the host immune system and other intestinal microbes including bacteria and worms. We recently discovered CD300lf as a receptor of MNV. We leveraged this finding to identify tuft cells as a target cell of MNV in the mouse intestines. Tuft cells are rare epithelial cells that sense and initiate an immune response against intestinal worms. Tuft cells are also important in regulating intestinal inflammation, wound recovery, and several mucosal cancers. In preliminary data, we developed novel tuft cell deficient mice and both CD300lf conditional knockout and knock-in mice to study the role of tuft cells during acute and chronic norovirus infection. W We also developed an in vitro MNV tuft cell culture system that will enable us to dissect the complex interactions between norovirus, tuft cells, and the immune system. The objectives of this proposal are to determine the role of tuft cells in norovirus infection, to determine the immunological consequences of tuft cell infection, and to discover how infected tuft cells evade CD8+ T cell killing. In Aim 1, we will determine if viral infection impairs tuft cell function. We will identify the role of tuft cells in acute and persistent MNV infection. We will determine how MNV kills tuft cells during chronic infection, how infection perturbs the tuft cell transcriptome, and whether virus infection of tuft cells impairs the ability of tuft cells to protect the host against worm infection. In Aim 2, we will determine the mechanism by which tuft cells act as an immunoprivileged niche for MNV. MNV-specific CD8+ T cells ignore infected tuft cells during chronic infection yet they remain functional and able to detect antigen ex vivo. We will identify how tuft cell tropism enables resistance to CD8+ T cells by combining novel mouse lines, viral genetics, tuft cell and T cell co-culture, and adoptive transfer of both tuft cell and MNV-specific CD8+ T cells. In particular, we will determine if quiescent long-lived tuft cells, a tuft cell subtype, are a novel immunoprivileged reservoir for chronic infection. We anticipate this work will generate a detailed understanding about the cell tropism regulating norovirus transmission, the role of viral infection in type II immunity, and the mechanism by which norovirus evades immune CD8+ T cells. This is critical to our long-term goal of deciphering mechanisms of human norovirus pathogenesis and developing a successful human norovirus vaccine.